Direct Evidence for the Dynamic Chromospheric Origin of Solar Coronal Plumes

Coronal plumes are long ray-like open structures in coronal holes, and have been considered as possible sources for the fast solarwind. Their origin in the largely unipolar coronal holes has long been a mystery. Earlier spectroscopic and imaging observationshave revealed blue-shifted plasma and propagating disturbances (PDs) in plumes that are widely interpreted in terms of flowsand/or propagating slow-mode waves, but these interpretations (flows vs waves) are under debate. Recently we discovered an important clue about plume internal structure: dynamic filamentary features called plumelets, which account formost of the plume emission. Here we present high-resolution observations from SDO/AIA and IRIS that revealed numerous quasiperiodic tiny jets (so-called jetlets") associated with transient brightening and plasma heating at the chromospheric footpoints of the plumelets. By analogy to larger coronal jets, these jetlets are most likely produced within the plume base by magnetic reconnection between closed and open flux at a stressed 3D null point. The jetlet-associated brightenings are in phase with plumelet-associated PDs, and vary with a period of 3 to 5 minutes, which is remarkably consistent with the photospheric/chromospheric p-mode oscillation. This reconnection at the open-closed boundary in the chromosphere/transition region is likely modulated or driven by local manifestations of the global p-mode waves. We discuss how these quasiperiodic jetlets extend upward to become plumelets, contribute mass to the solar wind, and may be sources of switchbacks recently detected by the Parker Solar Probe.